Prior to the present invention, the equipment for measuring axial forces has been taught in the prior art. See, for example, publication WO 86/02323, especially FIG. 3. This publication describes equipment for measuring axial forces which utilizes an electric contact member which closes when the elastomer-type spring element has been compressed by a particular given dimension. This elastomer-type spring element is compressed under the impact of such axial force. One serious drawback with this prior art axial force measuring equipment is that such equipment will only indicate that an axial force is present. Furthermore, such equipment only indicates that this axial force has reached a predetermined force or that such axial force has exceeded such predetermined force. In other words, the actual axial force being exerted on such equipment cannot be measured with any degree of accuracy.
It should be obvious, therefore, that such equipment is not suitable for use in situations where some reaction will be required. This is particularly the case if such reaction corresponds to the size of the axial forces being encountered.
Also, it is known in the prior art from German publication DE 27 52 641 A1, that signals can be generated at a coupling. Such signals are generated in conjunction with a mechanical spring element, for various sizes of axial forces, which is combined with multiple-step switches. The switching steps of such multiple-step switches in this prior art mechanism are activated successively with an increasing spring action of such mechanical spring element. Further, this publication suggested the use of a multiple-step switch in combination with an elastomer spring element, as is currently known prior to the present invention. A logical extension of such above-described solution could be the replacement of the multiple-step switch with a linear-type sensor, for example. It is recognized that an elastomer spring element possesses the capability of indicating in a progressive manner the spring reaction as it is subjected to ever-increasing loads. As will be recognized by persons skilled in the art, signals generated at a coupling in the above-described manner have a number of disadvantages. For example, applications utilizing either the multiple-step switch or the linear sensor will exhibit, as far as the spring element itself is concerned, the disadvantage of decreased or loss of precision and resiliency with increasing axial forces being exerted thereon. Another highly significant disadvantage of such signals generated at the coupling in this manner is the non-linear path of such generated signals.
Further adding to the problems of the prior-art-type equipment used to measure the axial forces being exerted on a component is the environment such equipment must operate in. This is particularly the situation when such equipment is being used to measure the axial forces being exerted on a coupling used to connect a pair of vehicles together.
Additionally, in these prior art axial force measuring devices, compensation for certain interferences which can be caused, for example, by temperature reactions of the elastomer spring element and its time reaction, that is, the setting effect cannot be readily achieved. The zero point shift of such elastomer spring element also constitutes such an interference.